D?-p? conjugation in Sn-O and Sn-S bonds of organotin compounds

Abstract

1. The coordination capacity of organotin compounds containing alkoxy and mercapto groups was investigated by the methods of cryoscopic, dielectrometric, and calorimetric titration. Oxygen- and sulfur-containing compounds behave differently with respect to the acceptors SnCl4 and (C4H9)2SnCl2. The former give stable complexes, while the latter do not form complexes. 2. The difference in the donor capacity of the heteroatoms in alkoxy- and mercapto derivatives of tin is explained by the presence of dπ-pπ conjugation in the Sn-S bonds and by its absence in Sn-O bonds. This conclusion was confirmed by an investigation of the electronic spectra and by quantum chemical calculations of the overlapping integrals. 3. The interaction of R2SnHal2 and R2Sn(XR)2 leads to the formation of complexes RSnHa · R2Sn(OR)2 in the case when X=0, and to the formation of the compound R2Sn(Hal)(SR) in the case when X=S. Dibutyltin (chloro)butylmercaptide was isolated and characterized. 4. The IR spectra of (C4H9)3SnSC4H9, (C4H9)2Sn(SC4H9)2, and (C4H9)2SnCl(C4H9) were taken in the region of 300–600 cm−1. The frequencies of the Sn-S and Sn-O vibrations were assigned.